1. Field of the Invention
This invention relates to electrical interconnect apparatus and more particularly to electrical interconnect apparatus between a flexible circuit and a printed circuit board.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
Electrical interconnections between parts of an electronic system are often made with flexible circuits, which are conventionally made with a polyester or polyimid material such as a Mylar or Kapton substrate onto which multiple conductors are deposited. It is often necessary to interconnect the electrical contacts on a flexible circuit to electrical contacts on a rigid printed circuit board. A high interconnect density, which is the number of interconnects per square area, is very desirable, because miniaturization of electronics is increasing requiring higher interconnect density.
There are a number of conventional approaches to accomplish the interconnection between a flexible circuit and a printed circuit board. One conventional approach is to simply solder the flexible circuit to the printed circuit board (PCB). This approach, however, has the disadvantages of: 1) low interconnect density, because it is necessary to maintain the spacing between interconnects to prevent solder bridging, and 2) the need to use Kapton, which is more tolerant to heat than Mylar. With this technique assembly and disassembly are inconvenient.
A second conventional approach is to solder a connector to the flexible circuit for connection with a connector soldered onto the PCB. This approach is easy to assemble and disassemble, but requires a connector on both the printed circuit board and the flexible circuit. In addition it requires a stiffener to be attached to the flexible circuit to support the connector, which increases the cost. It also has the disadvantage of achieving only low interconnect density.
A third conventional approach uses high pressure to force the flat contacts of a flexible circuit onto the contacts of a printed circuit board. This approach has the disadvantage that a rigid structure is required to support the high pressure. In addition, this approach is limited in that it requires the contacts on the PCB to be above the surface of the PCB. Often a coating such as a solder mask is applied over a PCB to protect the conductors from solder bridging and moisture. This coating leaves the exposed contacts on the PCB slightly recessed below the surface of the PCB, which makes connection with the contacts difficult. The high pressure approach also has the disadvantage of high cost.
A fourth conventional approach is to use spring fingers which are soldered onto the PCB. The flexible circuit is pressed onto the spring fingers to make contact. This approach has the shortcomings of high cost and low interconnect density, because of the space requirements for soldering the spring fingers to the PCB.
Another technique that has been used is called a zebra stripe and consists of an elastomer having alternating conductive and nonconductive sections. The zebra stripe is placed between a flexible circuit and a PCB and then the entire assembly is pressed together to complete the interconnect. This approach has the shortcomings of low interconnect density, high cost, and low reliability.
Accordingly, there is a need in the art for an improved interconnect system that provides higher interconnect density, reduced cost and increased reliability compared to conventional interconnect systems and which is also easy to assemble and disassemble.